The fundamentals
Working principle
Flow batteries were initially developed in the 1960s by The USA’s National Aeronautics and Space Administration, better known simply as NASA. But it wasn’t until the 1980s that their popularity picked up speed, after they were proven to last for more than 10,000 charge/discharge cycles. Along with the continuously growing installed base of renewable energy systems, most notably solar and wind power, it has become obvious that the need to store large, indeed very large, quantities of electrical energy for longer periods of time is growing equally quickly. Such energy storage is essential if we are to achieve a total transition from fossil fuels to renewable energy.
The term flow battery covers a family of storage systems where each one will apply the same fundamental working principle, while using different combinations of active materials. The heart of a flow battery is a so-called electrochemical cell, which is a multi-layer assembly of an ion-selective membrane, catalyst layers and electrodes.
A complete flow battery system, also referred to as a redox flow battery or RFB, is constructed around such electrochemical cells, where chemical energy is provided by the chemical reaction of two active materials. The active materials are contained within the system, separated by the membrane, and circulate in a closed loop, each one in their own respective space.
When an electrical power source is connected, which is when the battery is charging, a chemical redox reaction starts. Ion exchange then occurs through the membrane, resulting in electric current. During discharge, when applying an electrical load, the reverse chemical reaction takes place.
The voltage of the electrochemical cell is determined by the Nernst equation and ranges in practical applications from 1.0 to 2.2 V, depending on the selected active materials.
In order to increase the total electrical power, individual electrochemical cells are stacked, which is another way to say that the cells are electrically interconnected in series. To design systems with (very) large power levels, multiple stack assemblies can be interconnected.
The power [MW] of a flow battery system, as depicted above, is determined by the surface area of the ion-selective membrane, while the capacity [MWh] of the system is determined by the volume of the catholyte and anolyte reservoirs.
The fact that the membrane surface area and the reservoir volumes can be dimensioned individually highlights one of the most distinguishing properties of flow batteries, as opposed to traditional electricity storage systems where power [MW] and capacity [MWh] scale simultaneously.
Enabling affordable green hydrogen for clean fuel production by applying Long-Duration Energy Storage
Author:
Dries Kleuskens (Business Developer)
Abstract
Green hydrogen production faces a critical design challenge: renewable electricity is intermittent, while clean-fuel processes such as ammonia, methanol and e-fuels require stable, high-utilization operation. With hourly RFNBO matching approaching, this mismatch will increasingly shape the economics of future clean-fuel hubs.
In this whitepaper, Elestor compares a traditional LFP + hydrogen storage configuration with an LDES-based hub design using Elestor’s hydrogen-iron flow battery upstream of the electrolyser. Based on 10 years of hourly solar and wind data for Ain Sokhna, Egypt, the modelled baseload case shows that a 36-hour Elestor flow battery can reduce LCOH by up to 20% by improving electrolyser utilization, reducing installed electrolyser capacity and avoiding separate downstream hydrogen storage.
Download the whitepaper to learn how long-duration energy storage can help make baseload green hydrogen supply more affordable, controllable and scalable.
Engineered for 25 Years: Commercial Durability Proven in Elestor’s Hydrogen–Iron Flow Battery Technology
Authors:
Kaan Colakhasanoglu (Stack Research Specialist)
Wiebrand Kout (CTO)
Abstract
Elestor’s hydrogen–iron flow battery architecture is put to the test and evaluated under continuous, commercially relevant operating conditions to assess durability, performance stability, and lifetime potential. The system combines a hydrogen gas circuit with an aqueous iron-based electrolyte, enabling independent scaling of power and energy while relying on abundant, low-cost active materials (±2.8€/kWh, enable reaching 15€/kWh CAPEX and 0.02€/kWh Levelized Cost of Storage at system level).
An extended continuous cycling campaign demonstrates stable operation at practical current density, temperature, and voltage windows representative of real-world deployment. Measured performance remains stable and fully recoverable through standard conditioning procedures. The absence of structural or electrochemical failure under sustained operation provides a robust empirical basis for extrapolating operational lifetimes of 20–25 years under standard use profiles.
This work positions hydrogen–iron flow battery technology as a durable, scalable, and economically viable solution for long-duration energy storage.
Energy Independence for Islands
Authors:
Willem de Vries (Charged Islands)
Mohamad Alameh (Charged Islands)
In cooperation with Floris van Dijk (Elestor)
Abstract
Due to recent declines in the cost of photovoltaic solar generators (PV) and battery energy storage systems (BESS), baseload renewable energy systems (BRES) can now outcompete a grey generation mode (diesel electricity generation) on a 24/7 basis. BRES now promise a 30% reduction in electricity generation costs compared to diesel generators for a wide set of geographies, often reducing generation costs by 100 EUR/MWh. This gap is expected to grow with the introduction of cheaper long duration energy storage (LDES) systems in the future, potentially reducing cost of electricity supply by 50% compared to diesel generation.
With economic arguments in favour of BRES, a movement towards deployment of such systems can be expected and is also encouraged and supported by the writers of this white paper.
Numerous islands will have to overcome various hurdles though trying to implement BRES. Examples of such hurdles are shortage of development & financing capabilities as well as the shortage of land and a lock-in of diesel generation assets.
Dutch hydrogen battery promises 2 cents per kWh and lasts for decades
Article on TW.nl: A Dutch breakthrough in battery technology could keep the electricity grid stable for decades, at low cost and as a sustainable alternative to lithium batteries. This hydrogen–iron flow battery could significantly reshape large-scale energy storage.
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Hydrogen-iron flow battery could deliver 25-year grid energy storage with 80% efficiency
Article on Interesting Engineering: A Dutch battery manufacturer has developed a revolutionary hydrogen-iron flow battery that could reportedly power grids for decades while maintaining stable efficiency across tens of thousands of charge-discharge cycles.
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Article and interview in Solar365 magazine: Elestor to build largest hydrogen battery ever
For the energy transition to succeed, sufficient renewable generation is required, but also the ability to store that energy for longer periods. Technologies capable of storing energy between eight and one hundred hours can play a crucial role. A broad consortium has received €22 million in funding from the Dutch National Growth Fund for the so-called SLDBatt project (Sustainable Long Duration Battery), which focuses on long-duration electricity storage.
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